There is proposed a method for image-forming which uses a photosensitive media sheet having a pressure-sensitive property, and an image-receiving sheet so as to reproduce picture images on the image-receiving sheet, as disclosed in the Japanese Patent Publication (unexamined) No. 88739/1983. The media sheet is composed of a film coated with a dispersion of three kinds of micro-capsules, thereby being sensitive to all kinds of colors as disclosed in the Japanese Patent Publication (unexamined) No. 30537/1983. These three kinds of micro-capsules are:
(1) a Y micro-capsule containing a photo-curable ingredient sensitive to light within a blue wavelength range, and a colorless dye capable of coloring to yellow; PA1 (2) an M micro-capsule containing a photo-curable ingredient sensitive to light within a green wavelength range, and a colorless dye capable of coloring to magenta; and PA1 (3) a C micro-capsule containing a photo-curable ingredient sensitive to light within a red wavelength range, and a colorless dye capable of coloring to cyan.
In this media sheet, each kind of micro-capsule is partially cured by exposure with picture image forming light within its own sensitive wavelength range. After the exposure, the media sheet and the image-receiving sheet are overlapped to each other at their active surfaces, under pressure, to crush the uncured micro-capsules, so that colored picture images can be reproduced on the image-receiving sheet.
There are two methods of exposing the media sheet sensitive to all kinds of colors, to picture image forming light. One is to simultaneously expose the media sheet to picture image forming light within a wavelength range of approximately 400 to 700 nm which includes red, green, and blue wavelength ranges, such as reflected light from a colored original document. The other is to successively expose the media sheet to the respective picture image forming light within a blue wavelength range of approximately 400 to 500 nm, within a green wavelength range of approximately 500 to 600 nm, and within a red wavelength range of approximately 600 to 700 nm, in accordance with the respective sensitivities of the Y, M, and C micro-capsules. In the method of the successive exposure, the digital picture image information which is read, for example, by an image scanner or the like can be printed as colored picture images. Such an example is given where the respective digital picture image information corresponding to yellow, magenta, and cyan are written to three liquid crystal plates, and a media sheet is first exposed only to light within a blue wavelength range transmitted through the liquid crystal panel to which the yellow picture image information is written, and then, exposed to the respective light transmitted through the liquid crystal panels to which the magenta, and the cyan picture image information are respectively written. The Y, M, and C micro-capsules on the media sheet are cured to form images corresponding to the digitized color picture image information.
It is to be noted that there arises a drawback that the densities of three primary colors of yellow, magenta, and cyan are decreased in the above mentioned three stepped exposure method. Furthermore, there occurs a severe difference in the characteristic curve between each of the reproduced primary colors and the reproduced neutral grey, which causes turbidity in the colors of the reproduced picture images. For this reason, the conventional digital picture image processing technique cannot reproduce color accurately.